Controlled release of antifoam additives from compounded rubber

ABSTRACT

A rubber composition contains an antifoam compound that leaches out of the rubber composition when placed in contact with a functional fluid. The antifoam compound is delivered into a functional fluid such as an automatic transmission fluid or an engine oil by contacting the functional fluid with the rubber composition. In addition to the antifoam compound, the rubber composition contains one or more elastomers, which may be selected from a wide variety of natural or synthetic rubbers. In a preferred embodiment, the elastomer comprises a high temperature elastomer such as acrylic elastomer and ethylene acrylic elastomer.

FIELD OF THE INVENTION

The present invention relates to rubber compositions containing siliconepolymers. More specifically, the invention relates to antifoam compoundsfor functional fluids, methods for formulating the fluids, and uses ofthe fluids in engines and transmissions.

BACKGROUND OF THE INVENTION

Automatic transmission fluids (ATF) are non-compressible lubricantcompositions containing a number of conventional additives. As typicallyused, an ATF serves as a hydraulic fluid, activating and engaging gearsin the transmission by a series of valves and other hydraulic circuits,and as a lubricant for the hydraulic pump used to provide hydraulicpressure for operation of the transmission. Engine oils are lubricatingfluids containing conventional antiwear, antioxidant, and otheradditives in a mineral oil or synthetic oil base.

ATF, engine oils, and other functional fluids generally containdetergent and similar additives that tend to produce foam if air isentrained into the fluid. Additionally, impurities are produced in thefluid over time (for example by oxidation or degradation of the baseoil), some of which may contribute to a foaming tendency in thefunctional fluid. Excess foam in a functional fluid can adversely affectits rheological, hydraulic, lubricating, and cooling performance.Entrained air in a hydraulic system fluid such as an ATF is a problemfor the further reason that the air alternately expands in the lowpressure inlet side of pump, and quickly contracts or is compressed asthe fluid passes through the pump to the high pressure outlet side.

The resulting implosion of air bubbles on the outlet side causespressure ripples in the hydraulic pump. The pressure ripples can causeobjectionable audible noise, manifested as “pump whine” in sometransmissions. New automatic transmissions, such as continuouslyvariable transmissions (CVT), with their compact sumps and high pumppressures, have raised the possibility of consumer reaction to thenoise. In response, a number of OEM's have taken steps to reduce the airlevel in the fluid of their new transmissions by isolating or bafflingthe internal rotating components to separate them from the fluid, or byintroducing aeration additives into the ATF to help the oil release theentrained air more quickly or otherwise reduce the level of entrainedair. Additionally, conventional antifoam agents have been employed tohelp dissipate surface air bubbles.

The insolubility of the antifoam agents leads to some difficulties thatmust be addressed by the formulator of functional fluids such as ATF andengine oils. Typically, the antifoam, agent is denser than the basefluids and tends to fall out during shipping and storage before beingadded to the transmission. In practice, this limits the amount ofantifoam agent that can be incorporated or dispersed into the fluid bythe supplier. Alternatively, a formulated fluid may be re-dispersedprior to use, but the extra step creates additional expense in themanufacturing process.

New methods for preparing functional fluids containing insolubleantifoam compounds are needed. It would be desirable to provide suchmethods for delivery of antifoam compounds into functional fluids suchas transmission fluids and engine oils in order to provide advantagesover prior art methods.

SUMMARY OF THE INVENTION

Methods of delivering an antifoam compound or compounds into afunctional fluid are provided through the use of a rubber composition.The rubber composition comprises an elastomer and an antifoam compoundthat leaches out of the rubber composition when placed in contact withthe functional fluid. The rubber composition is placed in contact withthe functional fluid (for example, an automatic transmission fluid or anengine lubricating oil), whereupon the antifoam compound leaches intothe functional fluid. The elastomer may be selected from the groupconsisting of natural rubber and synthetic rubber, and advantageouslycomprises a high temperature elastomer. The antifoam compound ispreferably selected from the group consisting of silicones, halogenatedsilicones, and perfluorinated silicones.

In another embodiment, an engine or automatic transmission is providedalong with methods for incorporating a rubber composition into thelubricant sump of the engine or transmission. The rubber compositioncontains an elastomer and antifoam compound as discussed above.

Methods for treating an engine or an automatic transmission withantifoam, for example to reduce pump whine in an automatic transmissioninvolve contacting the functional fluid in the engine or transmissionwith a rubber composition that contains an antifoam compound thatleaches out upon contact with the fluid. Preferably, an amount ofantifoam compound leaches from the rubber composition to deliver from0.0005% (5 ppm) to 1% by weight of the antifoam compound to thefunctional fluid.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The term functional fluid refers to a liquid composition, typically foruse in industry, into which it is desirable or necessary to add anantifoam compound. As conventionally used, the term characterizes thefluid by the function it carries out. Non-limiting examples offunctional fluids include transmission fluids, engine oils, hydraulicfluids, lubricating fluids, heat transfer fluids, brake fluids, coolingfluids, and the like.

In one embodiment, the method of the invention provides a rubbercomposition containing an antifoam compound that leaches out of therubber composition when placed in contact with a functional fluid.Methods for delivering an antifoam compound into a functional fluid arealso provided, comprising contacting the functional fluids with therubber composition. In addition to the antifoam compound, the rubbercomposition also contains an elastomer which may be selected from a widevariety of natural or synthetic rubbers. In a preferred embodiment, theelastomer comprises a high temperature elastomer such as acrylicelastomers and ethylene acrylic elastomers.

In another embodiment, a method for delivering an antifoam compound intoan engine or an automatic transmission in the sump of the engine orautomatic transmission is provided. The method includes installing arubber composition into the sump of the transmission or engine andadding a fluid to the sump to contact the rubber composition. Uponcontact with the fluid in the sump, the antifoam compound in the rubbercomposition leaches from the composition into the fluid.

In a preferred embodiment, an automatic transmission is providedcontaining a housing defining a lubricant sump. A rubber compositionsuch as described above is installed into the lubricant sump, andantifoam compound leaches out of the rubber composition when contactedwith the automatic transmission fluid. Methods for reducing unwantednoise or pump whine in an automatic transmission comprise the step oftreating the automatic transmission fluid with an antifoam compound byplacing the automatic transmission fluid in contact with a rubbercomposition as described above. While in contact with the fluid,antifoam compound leaches from the rubber composition into thetransmission fluid. The resulting reduction in foam leads to a lesseningof unwanted cavitation or pump whine noise.

The rubber composition may be provided in the form of a seal used in anautomatic transmission. Seals include, without limitation, gaskets,O-rings, and other sealing members. In another embodiment, the rubbercomposition is used in contact with the transmission fluid, but does notact as a seal in the automatic transmission. In this embodiment, therubber composition may be placed anywhere in the transmission system incontact with the transmission fluid.

In another embodiment, an engine, preferably an automobile engine, isprovided containing a rubber composition as described above installed inthe sump. Methods for reducing foam in the engine comprise placing alubricating oil in contact with the rubber composition in the sump,whereupon antifoam compound leaches into the engine oil.

Preferred antifoam compounds include silicones, halogenated silicones,and perfluorinated silicones. As used herein, the terms silicones andpolysilicones refer to siloxane polymers, also called polysiloxanes. Thepolymers are characterized by having alternating silicon and oxygenatoms in the polymer backbone, as described further below. Blends ofantifoam compounds may be used, as long as the antifoam properties of afluid treated with the antifoam compounds is not adversely affected.

Generally, silicones are polymers having backbone repeating units ofstructure

In the structure, R₁ and R₂ are independently selected from the groupconsisting of methyl, C₂₋₁₈ alkyl groups, phenyl, C₇–C₁₈ aryl alkylgroups, and C₇–C₁₈ alkyl aryl groups. As used here, the term aryl alkylrefers to alkyl substituted phenyl rings and alkyl aryl refers to alkylgroups that are substituted with phenyl rings. The phenyl rings maythemselves be further substituted with alkyl groups. In the case of thewell known polydimethyl silicones, R₁ and R₂ are both methyl.

Preferred embodiments include dimethyl siloxane polymers, phenylmethylsiloxane polymers, and diphenyl dimethyl siloxane copolymers.

The silicones can be modified to impart organic characteristics to theinorganic structure. Such may be desirable to make them more or lesscompatible with organic materials such as petroleum oils. For example,the methyl group of polydimethyl siloxane may be replaced with longerchain aliphatic or aromatic moieties. The polymethylalkyl siloxanes maybe provided as copolymers or homopolymers. Non-limiting examples includepolymethyloctadecyl siloxane, a copolymer of 70% dimethyl and 30%methyloctadecyl siloxane, polymethyltetradecyl-siloxane, a terpolymer of70% dimethyl, 15% dodecyl, and 15% tetradecyl siloxane, a terpolymer of50% dimethyl, 25% dodecyl, and 25% tetradecyl siloxane,polymethylhexadecyl-siloxane, and the like.

In addition to the repeating units having a structure as describedabove, the polysilicone of the invention also contains end groups. In apreferred embodiment, the end groups are trialkylsilyl andtrialkylsiloxy.

In another embodiment, the antifoam compounds comprise halogenatedpolysilicones characterized by backbone repeating units of structure

In the structure, at least one of R₃ and R₄ is —C_(n)H_(y)X_(2n+2−y),wherein n is from 1 to 20, y is greater than or equal to 0 and less thanor equal to 2n+2, and X is Cl, Br, or F.

In a preferred embodiment, the halogenated polysilicones containfluorine. In the structure above, X is F. Perfluorinated polysiliconesare those containing at least a —CF₃ group. The term perfluorinated isalso used to refer to those where y is zero in the above definition ofR₃ and R₄. In a preferred embodiment, at least one of R₃ and R₄ is—CH₂—CH₂—C_(m)F_(2m+1), wherein m is from 1 to 10. In a particularlypreferred embodiment, m is 1 and at least one of R₃ and R₄ is atrifluoropropyl group —CH₂—CH₂—CF₃. Trifluoropropyl substitutedpolysilicones are commercial available, for example, under the tradename FS-1265 of Dow Corning. The halogenated silicones may also containrepeating units of

as described above.

The silicones, halogenated silicones, and perfluorinated silicones arewell known in the art and are described for example in Encyclopedia ofPolymer Science and Engineering, Vol. 15, pp. 234ff (John Wiley & Sons1985), the entire disclosure of which is herein incorporated byreference. The antifoam compounds can be characterized as containingrepeating units such as those described above. In addition, they may bedescribed as copolymers obtained from hydrolysis of mixtures oforganochlorosilanes or other readily hydroylzable silanes. Blockcopolymers may also be prepared by known methods, for example fromreaction of linear polydimethylsiloxanes having silanol end groups witha disilylphenylene diol. Silicone organic polymers may also be preparedby copolymerizing a silicone polymer with an organic polymer, either bycopolymerization or by grafting pre-polymerized segments. Examples oforganic polymers that may be used to produce silicone organic copolymersinclude, without limitation, polyethers, polyesters, epoxies,phenol-formaldehyde resins, and acrylic resins.

Silicones of the invention, including halogenated and perfluorinatedsilicones, may be prepared as homopolymers such as polydimethyl siloxaneand homopolymers of methyl trifluoropropyl siloxanes. In addition,polymethyl alkyl siloxanes may be prepared by hydrosilation reactions,where a desired olefin adds Si—H provided by an acid-equilibratedpolymethyl hydrogen siloxane.

Variations in the structures of the silicones, halogenated silicones,and perfluorinated silicones discussed above may also be accommodated inthe antifoam compounds of the invention. If present, such variations andmodifications should be such that they do not adversely affect theantifoam activity of the antifoam compound in a functional fluid. Withthis proviso, antifoam compounds having a wide range of molecularweights and additional reactive or non-reactive groups may be used.

For example, the perfluorinated silicone Dow Corning FS-1265 has astructure that can be represented as

FS-1265 is commercially available in at least two molecular weights. Inthe first, the molecular weight is from 4300–9700. In the formula, n isfrom 26–62, and the antifoam compound has a viscosity of approximately1000 centistokes. In another commercial embodiment, FS-1265 has amolecular weight of from 9400 to 37,300. In this embodiment, n in theformula above is from 59 to 238, and the antifoam compound has aviscosity of approximately 10,000 centistokes.

The rubber compositions of the invention contain the antifoam compoundor compounds in addition to conventional elastomers and other compounds.Compounded rubbers and methods for their preparation are well known. Seefor example the general discussion given in Chapter 2 of RubberTechnology, Third Edition, edited by Maurice Morton (Van NostrandReinhold Company, 1987), the disclosure of which is herein incorporatedby reference.

Conventional rubber composition additives include elastomers, processingaids, vulcanization agents, accelerators, accelerator activators, ageresistors (antidegradants), fillers, softeners, and miscellaneousingredients. The basic component of rubber compositions is elastomer. Itmay be provided in the form of rubber alone, or as masterbatches ofrubber and oil, rubber and carbon black, rubber-oil-carbon black, andthe like. Combinations or blends of elastomers may be used, so that therubber composition contains one or more elastomers. The elastomers areselected in order to obtain the specific physical properties desired inthe final product.

A wide variety of natural and synthetic rubbers is available for use asthe elastomers in the rubber compositions of the invention. Naturalrubber consists essentially of cis-1,4-polyisoprene, and is availablefrom a variety of natural sources. Synthetic rubbers include syntheticpolyisoprene and a number of other rubber materials that have beendeveloped over the years. Non-limiting examples of synthetic rubbersinclude acrylic elastomers, acrylonitrile butadiene elastomer (NBR),butyl rubber (IRR), isobutylene-isoprene elastomer, chlorinatedpolyethylene elastomer (CM, CPE), chlorosulfonated polyethylene (CSM),epichlorohydrin elastomer, ethylene-propylene copolymer (EPM),ethylene-propylene-diene terpolymer (EPDM), ethylene/butene elastomer,ethylene/octane elastomer, ethylene/vinylacetate copolymer,isobutylene-paramethylstyrene elastomer (IMS), polybutadiene elastomer(BR), polychloroprene (CR), polyisobutylene, polyisoprene (IR),polynorbornene (PNR), and styrene-butadiene rubber (SBR). For hightemperature applications, such as in automatic transmissions fluids,acrylic elastomers (ACM) and the ethylene acrylic elastomers areparticularly suitable.

Acrylic elastomers (ACM) are copolymers based on a backbone containingrepeating units of acrylic monomers (about 95–99%) and a so-calledreactive cure site monomer (about 1–5%). Crosslinking or “vulcanization”is dependent on the reactivity of the cure site monomer. Acrylicmonomers include alkyl esters such as ethyl acrylate and butyl acrylate,and alkoxy esters such as methoxy ethyl acrylate and ethoxy ethylacrylate. The cure site monomer is usually proprietary to a particularsupplier. In ACM resins, the cure site typically has a halogen,especially chlorine functionality, that allows for crosslinkingreactions to occur. Acrylic elastomers are resistant to oils at elevatedtemperatures and to aliphatic hydrocarbons. As such, they are preferredas the elastomer component of rubber compositions in contact with oilbased functional fluids such as automatic transmission fluids. Acrylicresins are commercially available, for example from Ethyl Corporationunder the Hitemp® trade name.

Ethylene acrylic elastomers are similar to acrylic elastomers, exceptthe backbone is generally based on ethylene and acrylic ester monomers,with a cure site typically based on a carboxylic acid. In oneembodiment, the acrylic ester is methyl acrylate, and the cure sitemonomer is a carboxylic acid functional monomer. They share the acrylicelastomer properties of resistance to oils and high temperatures.Ethylene acrylic elastomers or rubbers are commercially available, forexample from DuPont under the Vamac® trade name.

The elastomers are the major component of most rubber compositions. In atypical recipe, the ingredients are normally given in amounts based on atotal of 100 parts of the elastomers making up the rubber composition.The elastomers are listed as 100, with the levels of other additivesbeing noted as parts per hundred parts rubber (phr).

Most rubber compositions must be crosslinked or vulcanized to developsuitable properties for their end use. To this end, vulcanization agentsare included in rubber composition recipes. The vulcanization agents maybe classified as sulfur or non-sulfur.

In one embodiment, the vulcanization agent contains elemental sulfur orother sulfur compound. Non-limiting examples of non-elemental sulfurcompounds include tetramethylthiuram disulfide, dipentamethylenethiuramhexasulfide, dimorpholinyl disulfide, dibutylxanthogen disulfide, andalkylphenol disulfide.

Most non-sulfur vulcanization agents belong to one of three groups: 1)metal oxides; 2) difunctional compounds; and 3) peroxides. Metal oxidesare particularly suitable for crosslinking carboxylated elastomers orchlorine containing elastomers such as polychloroprene andchlorosulfonated polyethylene. Non-limiting examples of useful metaloxide vulcanization agents include zinc oxide, letharge (PbO), blends ofletharge and magnesia (MgO) and combinations of magnesia andpentaerythritol.

Difunctional compounds act as vulcanizing agents by reacting withfunctional groups to form crosslinks. For example, epoxy resins may beused with nitrile rubbers, phenolic resins or quinonedioximes may beused with butyl rubber, and diamines or dithio compounds withfluororubbers.

Organic peroxides may be used to crosslink rubbers that contain nodouble bonds or that do not contain other reactive groups capable offorming crosslinks with a difunctional compound. Non-limiting examplesof peroxide vulcanization agents include dicumyl peroxide,2,5-bis(t-butylperoxy)-2,5-dimethylhexane, and zinc peroxide.

Accelerators may be used in rubber recipes to accelerate the rate ofcure and/or reduce the temperature at which cure occurs. Non-limitingexamples of accelerators, listed from slow to fast, include aniline,diphenylguanidine, hexamethylene tetramine, mercaptobenzothiazole,benzothiazyl disulfide, thiurams, dithiocarbamataes, and xanthates.Accelerator activators may be used to activate the accelerator so itperforms more effectively. Commonly used accelerator activators include,without limitation, an inorganic compound such as zinc oxide, lime,letharge, red lead, white lead, magnesium oxide, alkaline carbonates,and hydroxides. Organic acids may be used in combination with the metaloxides. Non-limiting organic acid examples include stearic, oleic,lauric, palmitic, and myristic acids, as well as hydrogenated palm,castor, fish, and linseed oils.

Age resistors or anti-degradants protect the rubber from degradationbased on interaction with ultraviolet light or environmental oxidants.Age resistors include antioxidants and antiozonants. A wide variety ofchemical compounds is available to protect the rubber compositions fromdegradation. Three main chemical families include secondary amines,phenolics, and phosphites.

Softeners are used as physical plasticizers to modify the physicalcharacters of the rubber. One important class of softeners is the esterplasticizers. Non-limiting examples include dicapryl phthalate, butylcuminate, dibutyl phthalate, butyl lactate, methyl ricinoleate, butyloleate, dibutyl sebacate, dioctyl phthalate, methyl oleate, andtricresyl phosphate. Other softeners or plasticizers include fattyacids, vegetable oils, petroleum products, pine tar products and resins.

In addition to the classes of additives above, miscellaneous ingredientsinclude abrasives, blowing agents, colorants, flame retarders,homogenizing agents, internal lubricants, odorants, and retarders. Thesemay be incorporated into the rubber composition to provide specificphysical or chemical properties.

Most rubber compositions also include fillers that color, reinforce,extend, and/or make cheaper the compositions. The two major classes offiller used are carbon blacks and non-black fillers. Non-black fillersinclude, without limitation, semi-reinforcing materials such as clays,extending fillers such as calcium carbonate, re-enforcing fillers suchas precipitated silica, and pigmenting fillers such as titanium dioxide.

The most common methods for incorporating and compounding ingredientsinto rubber compositions involve the use either of a mill or an internalmixer such as a Banbury mixer. Mills and mixers for rubber compoundingare commercially available. Typical laboratory recipe and mixingschedules have been developed by a number of industry groups, such ascommittee D11 on rubber and rubber like materials of the AmericanSociety for Testing and Materials (ASTM).

The rubber compositions of the invention may be used to deliver anantifoam compound to a functional fluid by placing the rubbercomposition containing the antifoam compound in contact with the fluid.Upon contact with the functional fluid, the rubber composition leachesthe antifoam compound so that a certain quantity of the antifoamcompound of the rubber composition is delivered into the fluid. The rateof leaching and the amount of antifoam compound leached depend on anumber of factors, including the compatibility between the elastomer andthe antifoam compound, the nature of the functional fluid, and thetemperature of use. Sufficient amounts of the rubber compositions of theinvention should be placed in contact with the functional fluid todeliver an effective antifoaming amount of the antifoam compound. In thecase of automatic transmission fluids or engine oils, it is preferred todeliver an amount of antifoam compound such that the total fluidcontains by weight 0.0005% to about 1% of the antifoam compound.Depending on the efficiency and rate of leaching, it may be desirable toprovide rubber compositions in contact with the fluid that contain somemultiple or excess of antifoam compound over that required to make upthe antifoam effective level.

In one embodiment, the rubber compositions of the invention may be usedas substitutes for rubber compositions that are already in the system tobe treated with antifoam compound. For example, in the case of automatictransmissions, the rubber compositions of the invention may replace thegaskets, seals, O-rings or other rubber compositions that are used inthe transmission. An advantage of this procedure would be that therubber compositions of the invention could be utilized without redesignof the transmission or its packaging.

In another embodiment, the rubber compositions of the invention are usedas coupons or other physical forms that are mounted or otherwise affixedsomewhere in the fluid sump so that they remain in contact with thefluid during use. Thus, they may be mounted in brackets or othermounting niches provided in the system to be treated. In an automatictransmission, brackets or other mounting apparatus may be provided inthe fluid sump defined by the housing of the transmission. In an engine,a rubber composition according to the invention may likewise be mountedor installed in the crank case, oil pan, or other location where it cancontact the lubricating fluid. Conventional packaging considerationsapply. Space for the coupon or other form, which can take any shapeneeded to fit inside the packaging environment, may be readily designed.In comparison to the embodiment where the rubber composition is used toreplace an existing rubber composition in the system, the currentembodiment will generally involve some effort and redesign to place therubber composition in the sump.

The invention may also be practiced by contacting the rubber compositionwith the functional fluid for a time sufficient to leach an effectiveamount of antifoam compound into the functional fluid. The rubbercomposition may then be removed from contact with the functional fluid.In a preferred embodiment, the rubber composition is left in contactwith the functional fluid during use.

Effective defoaming capability of the antifoam compounds of theinvention depends in part on their insolubility in the process medium inwhich it acts. The antifoam additive is dispersed as a second liquidphase. The second phase has a tendency to segregate itself to reside atliquid air interfaces, including bubbles, due to its limited solubility.Although the insoluble nature of the antifoam compounds leads to itsantifoam performance, the insolubility imposes limitations on themaximum concentration that can be blended into a stable dispersion withsuitable shelf life for commercial use. The antifoam compounds of theinvention may be blended into automatic transmission fluid with highshear blending processes to mix in a limited concentration of antifoamagent. It is also possible to make supplemental additions, or “toptreats” of the antifoam compounds of the invention directly into theautomatic transmission. In a preferred method, an antifoam compound isdelivered into a functional fluid, such as an automatic transmissionfluid, by leaching into the fluid upon contact of fluid with a rubbercomposition containing the antifoam compound. However antifoam is added,it is preferred to use an antifoam compound having a viscosity in therange of about 1–150,000 centistokes to allow for ready blending anddispersal into the functional fluid.

Treat levels of the antifoam compound of the invention should be as lowas practical to avoid excessive costs, but should be at levelssufficient to reduce the foam in a functional fluid and/or thecavitation or pump whine noise associated with the foam in, for example,an automatic transmission. Generally, the antifoam should be deliveredin such an amount that it will be present in a functional fluid at alevel from about 5 ppm (0.0005%) to about 1% by weight. More preferably,the upper level of antifoam compound is about 0.5%, and more preferablythe fluid contains up to 0.3% by weight of the antifoam compound. In apreferred embodiment, antifoam compound is delivered to an automatictransmission fluid at a level of 0.0005% to 0.269% by weight. Toillustrate, in a continuously variable transmission having a sump volumeof 8 liters, for example, 3 g of delivered antifoam compound results ina treat level of about 0.05% of the antifoam compound assuming the ATFhas a density of ˜0.8.

The treatment level of antifoam compound in functional fluids will beinfluenced by the presence of other performance additives in the fluid,especially as the other additives affect the amount of air entrainmentin the fluid. Examples of such additives include pour point depressants,viscosity index improvers, antioxidants, corrosion inhibitors, extremepressure agents, antiwear agents, and other antifoam agents.

A variety of functional fluids may be used in the practice of theinventions. For illustrative purposes and not by way of limitation, theinvention will now be further described for use in ATF. Blendedautomatic transmission fluids containing the antifoam compositions ofthe invention must generally exhibit a flash point greater than about170° C., withstand oxidation, suppress volatilization, and resistbreakdown. Further, the blended ATF must exhibit non-foamingcharacteristics at high temperatures and pressures and low viscosity atlow temperatures.

In addition to the base lubricating oil and the antifoam compounds,formulated ATF contain a number of other conventional additives such as:

-   -   boronated or non-boron dispersants;    -   anti-oxidation compounds;    -   seal swell compositions;    -   friction modifiers;    -   extreme pressures/antiwear agents;    -   viscosity modifiers;    -   pour point depressants; and    -   detergents.

The automatic transmission fluid should meet or exceed thespecifications of the car manufacturer. An example of a suitable ATF isGM DEX-CVT®, which is a continuously variable transmission fluid meetingboth GM 10028N and GM 9986220 specifications.

The base oils used in forming the automatic transmission fluids of thisinvention can be any suitable natural or synthetic oil having thenecessary viscosity properties. Thus, the base oil may be composedentirely of a natural oil such as mineral oil of suitable viscosity orit may be composed entirely of a synthetic oil such as apoly-alpha-olefin of suitable viscosity. Likewise, the base oil may be ablend of natural and synthetic base oils provided that the blend has therequisite properties for use in the formation of an automatictransmission fluid. Ordinarily, the base oil should have a kinematicviscosity in the range of 2 to 50 centistokes, preferably 3 to 8centistokes (cSt), at 100° C. Preferred base oils are Group III stocks.A preferred base oil viscosity is, for example, 3.8 cSt for the ratio ofVHVI 2 and VHVI 4 that is used. In an embodiment of the presentinvention, the individual viscosities of those base stocks are 2.8 cStand 4.3 cSt, respectively.

ATF of the invention preferably contain detergent and dispersants. Theyfunction in part to solubilize fluid components and to suspend insolublematerials that build up over time during operation. In one embodiment,the detergent/dispersant contains a first component (such as anN-aliphatic alkyl substituted diethanolamine) and a second componentcomprising either an oil-soluble phosphorus containing ashlessdispersant and/or at least one oil-soluble boron-containing ashlessdispersant. The ashless dispersants are present in amount such that theratio of boron in the ashless dispersant is in the range of about 0.05to about 0.2 part by weight of boron per part by weight of the firstcomponent, or the ratio of phosphorus in the ashless dispersant is about0.1 to 0.4 parts per part by weight of the first component.

In one embodiment, the compositions of this invention contain at leastone oil-soluble phosphorus- and boron-containing ashless dispersantpresent in an amount such that the ratio of phosphorus to the firstcomponent is in the range of about 0.15 to about 0.3 part by weight ofphosphorus per part by weight of the first component, and such that theratio of boron in the ashless dispersant is in the range of about 0.05to about 0.15 part by weight of boron per part by weight of the firstcomponent.

Phosphorus- and/or boron-containing ashless dispersants can be formed byphosphorylating and/or boronating an ashless dispersant having basicnitrogen and/or at least one hydroxyl group in the molecule, such as asuccinimide dispersant, succinic ester dispersant, succinic ester-amidedispersant, Mannich base dispersant, hydrocarbyl polyamine dispersant,or polymeric polyamine dispersant.

The ATF also contain antiwear agents in a level suitable for protectingthe moving components (e.g., the pump and the gears of the transmission)from wear. Typically, the antiwear additives will be present at a levelof about 0.025 to about 5% by weight of the ATF. A non-limiting exampleof a suitable antiwear agent is 2,5-dimercapto-1,3,4-thiadiazole (DMTD)or derivatives thereof. To illustrate, derivatives of DMTD include:

-   -   a) 2-hydrocarbyldithio-5-mercapto-1,3,4-thiadiazole or        2,5-bis-(hydrocarbyldithio)-1,3,4-thiadiazole and mixtures        thereof;    -   b) carboxylic esters of DMTD;    -   c) condensation products of halogenated aliphatic monocarboxylic        acids with DMTD;    -   d) reaction products of unsaturated cyclic hydrocarbons and        unsaturated ketones with DMTD;    -   e) reaction products of an aldehyde and diaryl amine with DMTD;    -   f) amine salts of DMTD;    -   g) dithiocarbamate derivatives of DMTD;    -   h) reaction products of an aldehyde and an alcohol or aromatic        hydroxy compound and DMTD;    -   i) reaction products of an aldehyde, a mercaptan and DMTD;    -   j) 2-hydrocarbylthio-5-mercapto-1,3,4-thiadiazole; and    -   k) products from combining an oil-soluble dispersant with DMTD;        and    -   mixtures thereof.

Compositions a)–k) are described, for example, in U.S. Pat. No.4,612,129 and patent references cited therein, the disclosures of whichare incorporated by reference. Thiadiazoles are commercially available,for example, from the Ethyl Corporation as HiTEC® 4313.

Depending on the base stocks that are chosen, an amount of seal swellagent may be required to meet the OEM seal compatibility requirements.Use of Group II, Group III and Group IV base oils many times requiresthe addition of a material to swell seals. These materials may be chosenfrom the general categories of oil-soluble diesters, aromatic base oils,and sulfones. Alkyl adipates are examples of soluble diesters that canbe used. In a preferred embodiment, alkyl adipate is used at a treatrate of 3% to 20%, more preferably −3% to 10%, and most preferably about5%.

A viscosity index (VI) improver is useful in the formulations andmethods of the present invention and can include, but is not limited to,one or more materials selected from polyacrylate, polymethacrylate,styrene/olefin copolymer, styrene diene copolymer, EP copolymer orterpolymers, and combinations thereof. A preferred VI improver is ahighly shear stable polymethacrylate polymer or copolymer used at, forexample, about 15% by weight in the fluid formulation. VI improvers arecommercially available.

The automatic transmission fluids of the invention may be used aslubricating compositions and hydraulic fluids in a variety of automotivetransmissions. In one embodiment, the transmission has a sump volume of13 liters (L) or less. In a preferred embodiment, the transmissions arecontinuously variable transmissions (CVT) with a sump of 9 L or less,preferably 8 L or less. One advantage of the ATF of the invention isthat they reduce foam or entrained air in an ATF. This has the effect ofreducing or eliminating the pump whine caused by the implosion of airbubbles on the pressure side of the pump. Because of the high pressuresinvolved, the problem is most pronounced in automatic transmissions ingeneral, and in CVT in particular. For this reason, in a preferredembodiment, the ATF of the invention are used as hydraulic andlubricating fluids in continuously variable transmissions. The CVT maybe configured as transmissions for rear wheel drive cars or astransaxles for front wheel drive cars.

The invention has been described above with respect to preferredembodiments. Further non-limiting description is given in the followingexamples.

EXAMPLES

The levels for all components except the fluorosilicone polymer aregiven, as is conventional, as parts per hundred rubber (phr). The levelof fluorosilicone polymer (antifoam compound) is given in % by weight ofthe entire rubber composition. The following components are used:

ethylene/acrylic elastomer A Vamac G (Dupont) ethylene/acrylic elastomerB Vamac GLS acrylic elastomer A Hitemp 4051 EP (Zeon) acrylic elastomerB Hitemp 4052 acrylic elastomer C Hitemp 4054 antioxidant Naugard 445(Uniroyal) activator/lubricant Stearic Acid (CP Hall) processingaid/dispersing agent Vanfre VAM (Vanderbilt) - ethoxylated octadecylalcohol, phosphate surfactant Armeen 18D (Akzo Chemical) filler Carbonblack plasticizer A TP-759 (Rohm and Haas) -di(butoxyethoxyethyl)adipate plasticizer B WB-222 (Struktol) vulcanizerA Diak #1 (Dupont) - hexamethylenediamine carbamate vulcanizer BRhenogran Diuron 80 (Rhein Chemie) vulcanizer C Hytemp NS70 (Zeon)accelerator Perkacit DPG (Ferro Corp.) - N,N′-diphenylguanidineflourosilicone polymer A FS-1265, 1,000 cSt (Dow Corning) fluorosiliconepolymer B FS-1265, 10,000 cSt

Component Example 1 Example 2 Example 3 Example 4 Example 5flourosilicone polymer A 12% 12% 12% 12% 12% flourosilicone polymer B 00 0 0 0 Ethylene/acrylic elastomer A 0 100 0 0 0 Ethylene/acrylicelastomer B 100 0 0 0 0 acrylic elastomer A 0 0 100 0 0 acrylicelastomer B 0 0 0 100 0 acrylic elastomer C 0 0 0 0 100 antioxidant 2 22 2 2 activator/lubricant 1.5 1.5 1 1 1 processing aid/dispersion agent1 1 0 0 0 Surfactant 0.5 0.5 0 0 0 Black 60 60 65 80 80 plasticizer A 1010 0 0 0 plasticizer B 0 0 2 2 2 vulcanizer A 1.5 1.5 0 0 0 vulcanizer B0 0 6 6 6 vulcanizer C 0 0 2 2 2 accelerator 4 4 0 0 0 Example ComponentExample 6 Example 7 Example 8 Example 9 10 flourosilicone polymer, 1,000cSt 0 0 0 0 0 flourosilicone polymer, 10,000 cSt 12% 12% 12% 12% 12%Ethylene/acrylic elastomer - A 0 100 0 0 0 Ethylene/acrylic elastomer -B 100 0 0 0 0 acrylic elastomer A 0 0 100 0 0 acrylic elastomer B 0 0 0100 0 acrylic elastomer C 0 0 0 0 100 antioxidant 2 2 2 2 2activator/lubricant 1.5 1.5 1 1 1 processing aid/dispersion agent 1 1 00 0 surfactant 0.5 0.5 0 0 0 Black 60 60 65 80 80 plasticizer - A 10 100 0 0 plasticizer B 0 0 2 2 2 vulcanizer A 1.5 1.5 0 0 0 vulcanizer B 00 6 6 6 vulcanizer C 0 0 2 2 2 accelerator 4 4 0 0 0

Rubber compositions according to the recipes given in Examples 1–10 areformulated into coupons. The coupons are installed into the sump of anautomatic transmission. Automatic transmission fluid is added to thesump to contact the rubber composition. Over time, antifoam compoundcomprising the flourosilicone polymer leaches into the transmissionfluid to provide a treat level of from 5 ppm to 1% by weight of theantifoam compound, based on the total weight of the transmission fluid.

1. A method for delivering an antifoam compound into a functional fluid,comprising contacting the functional fluid with a rubber composition,wherein the rubber composition comprises a compounded rubber thatcomprises an elastomer and further comprises an antifoam compound thatleaches into the functional fluid upon contact of the rubber compositionwith the fluid.
 2. A method according to claim 1, wherein the elastomercomprises an elastomer selected from the group consisting of an acrylicelastomer and an ethylene acrylic elastomer.
 3. A method according toclaim 1, wherein the antifoam compound comprises a fluorosiliconepolymer having a backbone and side chain, wherein the backbone comprisesrepeating —Si—O groups and the side chains comprise fluorine atoms.
 4. Amethod according to claim 3, wherein the fluorosilicone polymercomprises a plurality of repeating groups of structure:

wherein n is from 1–10, and R is C₁₋₆ alkyl.
 5. A method according toclaim 4, wherein n is
 1. 6. A method according to claim 4, wherein n is1 and R is methyl.
 7. A method according to claim 1, wherein theantifoam compound comprises a silicone polymer having repeating unitsof:

in the backbone, wherein R₁ and R₂ are independently methyl, C₂₋₁₈alkyl, phenyl, C₇–C₁₈ aryl alkyl, or C₇₋₁₈ alkyl aryl.
 8. A methodaccording to claim 7, wherein R₁ and R₂ are methyl.
 9. A methodaccording to claim 1, wherein the antifoam compound comprises at leastone group in its backbone having a structure:

wherein at least one of R₃ and R₄ comprises —C_(n)H_(y)X_(2n+2−y),wherein n is from 1–20, y is greater than or equal to 0 and less than orequal to 2n+2, and X is Cl, Br, or F.
 10. A method according to claim 9,wherein X is F.
 11. A method according to claim 9, wherein at least oneof R₃ and R₄ is —CH₂—CH₂—C_(m)F_(2m+1), wherein m is from 1–10.
 12. Amethod according to claim 9, wherein at least one of R₃ and R₄ is—CH₂—CH₂—CF₃.
 13. A method according to claim 1, wherein the functionalfluid is an automatic transmission fluid.
 14. A method according toclaim 1, wherein the functional fluid is an engine oil.
 15. A method fordelivering an antifoam compound into an automatic transmission fluid inthe sump of an automatic transmission, comprising: installing a rubbercomposition into the transmission sump; and adding an automatictransmission fluid to the sump to contact the rubber composition;wherein the rubber composition comprises: one or more elastomersselected from the group consisting of natural rubber and syntheticrubber; and an antifoam compound that leaches out of the rubbercomposition when placed in contact with the transmission fluid.
 16. Amethod according to claim 15, wherein the rubber composition is used asa seal in the automatic transmission.
 17. A method according to claim15, wherein the rubber composition is in contact with the transmissionfluid, but does not act as a seal in the automatic transmission.
 18. Amethod according to claim 15, wherein the antifoam compound comprises acompound selected from the group consisting of polysiloxanes,halogenated polysiloxanes, and perfluorinated polysiloxanes.
 19. Amethod according to claim 15, wherein the elastomer comprises anelastomer selected from the group consisting of an acrylic elastomer andan ethylene acrylic elastomer.
 20. A method according to claim 15,wherein the transmission is a continuously variable transmission.
 21. Amethod for delivering an antifoam compound into an engine oil in thesump of an engine, comprising: installing a rubber composition into theengine sump; and adding an engine oil to the sump to contact the rubbercomposition, wherein the rubber composition comprises: one or moreelastomers selected from the group consisting of natural rubber andsynthetic rubber; and an antifoam compound that leaches out of therubber composition when placed in contact with the transmission fluid.22. A method according to claim 21, wherein the antifoam compoundcomprises a compound selected from the group consisting ofpolysiloxanes, halogenated polysiloxanes, and perfluorinatedpolysiloxanes.
 23. A method according to claim 21, wherein the elastomercomprises an elastomer selected from the group consisting of an acrylicelastomer and an ethylene acrylic elastomer.
 24. A method according toclaim 21, wherein the antifoam compound comprises at least one group inits backbone having a structure:

wherein at least one of R₃ and R₄ comprises —C_(n)H_(y)X_(2n+2−y),wherein n is from 1–20, y is greater than or equal to 0 and less than orequal to 2n+2, and X is Cl, Br, or F.
 25. A method according to claim24, wherein X is F.
 26. A method according to claim 24, wherein at leastone of R₃ and R₄ is —CH₂—CH₂—C_(m)F_(2m+1), wherein m is from 1–10. 27.A method according to claim 24, wherein at least one of R₃ and R₄ is—CH₂—CH₂—CF₃.